Cordless, hand-held, battery-driven power tools use a battery pack as a power source. The battery pack includes a battery case in which a plurality of battery cells is accommodated.
In performing driving operations of the hand-held power tools, a user has to hold the power tool. Hence, it is required that such a power tool be light in weight, compact in size and have an easy-to-grasp grip portion.
FIGS. 1A to 1C show one conventional power tool 101 and a battery pack 105 used therein. FIG. 1A is a side cross-sectional view showing a conventional power tool 101. FIG. 1B is a side cross-sectional view showing a battery pack 105 mounted on the power tool 101 shown in FIG. 1A. FIG. 1C is a cross-sectional view of the battery pack 105 taken along a line IC-IC in FIG. 1B. The power tool 101 has a housing 102. The housing 102 includes a body portion 102A and a grip portion 102B. A motor 103 is housed in the body portion 102A. The motor 103 has a rotational shaft extending horizontally and coupled to an output shaft 104 via a speed reduction mechanism also housed in the body portion 102A. The motor 103 is energized when a switch 106 is turned on.
As shown in FIG. 1C, the battery pack 105 includes a battery case 107 into which three battery cells 108 are accommodated. Each battery cell 108 is of a generally cylindrical shape having a circular cross-section. Two battery cells 108 are disposed in side-by-side on the bottom of the case 107 and the remaining one battery cell 108 is placed above the two battery cells. Stated differently, three battery cells 108 are horizontally arranged and the battery pack 105 is mounted on the grip portion 102 in such a way that the case 107 is protruded from the bottom of the grip portion 102B by a height h′. Accordingly, while the grip portion 102B can be made thin, the vertical size of the power tool 101 is made large.
FIGS. 2A to 2C show another conventional power tool 201 and a battery pack 205 used therein. FIGS. 2A to 2C correspond to FIGS. 1A to 1C, respectively. The same reference numerals used in FIGS. 2A to 2C denote the same components described with reference to FIGS. 1A to 1C.
As shown in FIGS. 2B and 2C, the battery pack 205 includes a battery case 207 into which three battery cells 108 are vertically arranged. The battery pack 205 is inserted into the inner space of the grip portion 102B. As a result, the overall size of the power tool 201 can be made compact. However, the grip portion 102B become thick as three vertically arranged battery cells 108 are accommodated in the grip portion 102B.
Japanese Patent Application Publication No. 2006-302759 discloses a battery pack in which accommodated are two vertically arranged battery cells and two horizontally battery cells. When the battery pack is mounted on the power tool, a part of the battery pack protrudes from the bottom end of the grip portion and the remaining part of the battery pack is inserted into the grip portion. The grip portion is not so thin as the user can easily and firmly grasp the grip portion.